Bacterial Growth (BE #2) Flashcards
Binary fission
asexual reproduction in bacteria
How does a bacterial cell ensure that the replicated chromosomes get where they need to to go during cell division?
The duplicated chromosomes attach to separate spots on the plasma membrane & then it divides.
Phases of bacterial growth in the lab - define:
lag
log
stationary
death
lag - cell numbers remain constant; cells are preparing to how.
log - cell numbers increase exponentially
stationary - cells become smaller; some produce endospores
death - cell numbers decrease exponentially
Why would a bacterial culture enter the stationary phase?
overcrowding; accumulation of waste; depletion of nutrients; pH change
Why don’t bacteria go through all the stages in nature the way they do in the lab?
In nature, bacteria are not confined (limited on space); not limited on nutrients, either. They live with other species, so one’s waste may be another’s energy source.
strict aerobe
die in the absence of oxygen
microaerophiles
like less oxygen & more carbon dioxide
facultative anaerobes
can grow in the presence or absence of oxygen; can switch their metabolism
aerotolerant anaerobes
don’t use oxygen, but are not killed by exposure to it.
obligate (or strict) anaerobes
die in the presence of oxygen
Give an example of a mesophilic bacterial species.
Any human pathogen (Staphylococcus aureus, Escherichia coli, Salmonella enterica)
mesophilic
human pathogens; like body temperature
psychrophilic
bacteria that continue to grow in the refrigerator (cold-loving)
thermophilic
bacteria that are not killed by boiling temperatures; endospore formers
acidophiles
acid loving - bacteria that grow best at a pH of 1 - 5.4. Ex. Lactobacillus - ferments milk
neutrophiles
most human pathogens are in this category; exist from pH 5.4 - 8.5
alkaliphiles
base loving - exist from 7.0-11.5;
Ex. Vibrio cholerae (causes cholera)
Most bacteria live in ___________ environments.
hypotonic (tonicity)
Bacteria are hypertonic to their environments.
halophiles
salt loving - inhabit the oceans
indirect measurements of microbes
Measures s property of the mass of cells then estimate the number of microbes.
1. turbidity - look for cloudiness in tube
- metabolic activity - indicates relative numbers
direct measurements of microbes
Give more accurate measurements of #s of microbes:
- direct counts -
- Coulter Counter - electronic counter; gives total count (living & dead)
* Direct Microscope Count - special slide w/grid is used to count
- Coulter Counter - electronic counter; gives total count (living & dead)
- plate count - bacterial colonies are viewed through a magnifying glass against a Quebec colony-counting grid (give viable count)
- filtration - liquid or air is drawn through a membrane filter by a vacuum. The pores are too small for microbial cells to pass thru, so they collect on the filter. The filter is then placed on a solid medium & is incubated. (counts viable cells)
synthetic medium
is prepared in a lab using precise materials or well-defined materials.
complex medium
contains reasonable familiar materials by varies slightly in chemical composition from batch to batch
selective media
encourages the growth of some bacteria, but suppresses the growth of others (ex. salt sugar allows for growth of Staphylococcus, but not Streptococcus)
